Monadic predicate calculus

In logic, the monadic predicate calculus (also called monadic first-order logic) is the fragment of first-order logic in which all relation symbols^{[clarification needed]} in the signature are monadic (that is, they take only one argument), and there are no function symbols. All atomic formulas are thus of the form ${\displaystyle P(x)}$, where ${\displaystyle P}$ is a relation symbol and ${\displaystyle x}$ is a variable.

Monadic predicate calculus can be contrasted with polyadic predicate calculus, which allows relation symbols that take two or more arguments.